1. Field of the Invention
The present invention relates to the field of fabrication of semiconductor devices. More specifically, the invention relates to the fabrication of resistors for integrated circuits.
2. Related Art
Consumer demand for smaller, more complex, and faster devices operating at high frequencies, such as wireless communications devices and Bluetooth RF transceivers, has in turn resulted in an increased demand for integrated circuit (“IC”) chips that can operate at higher frequencies. For IC chips to be able to operate at higher frequencies, such as frequencies above 10.0 GHz, the electronic circuits in the IC chips, and the electronic components that form the electronic circuits, must also be able to operate at higher frequencies. However, as the frequency of operation increases, unwanted capacitance, i.e. parasitic capacitance, in IC chip components, such as resistors, can also undesirably increase. Thus, for example, IC chip manufacturers are challenged to fabricated IC chips having resistors with reduced parasitic capacitance.
In a conventional IC chip, polysilicon resistors are commonly used, and may be fabricated using metal oxide semiconductor (“MOS”) technology. For example, a polysilicon resistor may be fabricated by depositing a polysilicon film on a field oxide region in the IC chip. The polysilicon film may be deposited, for example, using a low-pressure chemical vapor deposition (“LPCVD”) process. The deposited polysilicon film may then be patterned and etched to form a resistor.
By way of background, capacitance develops, for example, when two plates made of an electrically conducting material are separated by a dielectric. The resulting capacitance is inversely proportional to the distance, or thickness, separating the two plates. In the polysilicon resistor, the polysilicon in the body of the resistor forms one plate of a capacitor. The silicon substrate, which is situated below the field oxide region, typically forms the second plate of the capacitor. The field oxide, which typically comprises a dielectric such as silicon dioxide, forms the dielectric for the above capacitor. Thus, a capacitance is developed between the polysilicon in the resistor and the silicon substrate of the IC chip. The value of the capacitance between the polysilicon resistor and the silicon substrate is inversely proportional to the distance between the polysilicon resistor and the silicon substrate. This capacitance is undesirable, i.e. parasitic, since a resistor should ideally have no capacitance. Since the polysilicon resistor is situated relatively close to the silicon substrate of the IC chip, the parasitic capacitance developed between the polysilicon resistor and the silicon substrate can be undesirably large, especially at frequencies above 10.0 GHz.
Other types of resistors used in a conventional IC chip include, for example, diffused, n-well, and p-well resistors. However, similar to polysilicon resistors discussed above, diffused, n-well, and p-well resistors suffer from a large parasitic capacitance due to the junctions that these resistors form with the silicon substrate.
Thus, there is a need in the art for a resistor having a reduced parasitic capacitance that can be fabricated in an IC chip.